U.S. Pat. No. 5,326,926 describes a process for isomerization of C4–C6 paraffins and for recovery of LPG-type hydrocarbons, essentially C4 hydrocarbons. This process comprises an isomerization followed by a stabilization column that produces a separation of the effluent obtained from the isomerization unit into 4 fractions and a stripping of one of the intermediate fractions to collect hydrocarbons that have 4 carbon atoms. This process does not include an absorption column.
Patent EP 0 488 757 B1 describes a process for isomerization of a flow that comprises C5–C6 hydrocarbons. Said process comprises an isomerization zone, a deisohexanization zone that provides at the top methyl and dimethylbutane and normal pentane that are sent to a selective adsorption unit in which the normal hydrocarbons are adsorbed, a lateral fraction comprising normal hexane and methyl pentanes recycled for isomerization and a fraction comprising hydrocarbons with a boiling point higher than that of normal hexane. A desorption stage allows recovery of normal hydrocarbons that are recycled in the isomerization unit. This process comprises adsorption and desorption stages, preferably by variation of pressure with a P.S.A. (Pressure Swing Adsorption according to English terminology, i.e., adsorption by pressure variation) but does not include an absorption stage. It no longer comprises a cooling stage and is optimized for separating the normal paraffins from isoparaffins after isomerization.
U.S. Pat. No. 5,238,555 describes a process for purification of hydrogen by treatment of an effluent containing hydrocarbons and hydrogen and obtained from a hydrocarbon conversion unit. This process comprises a fractionation of the effluent into a liquid phase and a vapor phase, followed by an indirect exchange in a gas/gas exchanger with a hydrogen-rich gas as far as the vapor phase is concerned and an exchange with a hydrocarbon-containing liquid as far as the liquid phase is concerned. The two liquid and vapor flows are then cooled in two separate cooling zones, then sent independently to said absorption unit that operates in countercurrent.